Low Temperature Cryostat

ABSTRACT

A low temperature cryostat is disclosed. The low temperature cryostat may include a cryostat vessel, a cooling device arranged in the cryostat vessel for producing a cooling temperature level, a microscopy device for examining a sample, and at least one thermal coupling for thermally and mechanically connecting the microscopy device to the cooling device. The cooling device may comprise a pulse tube cooling system.

RELATED APPLICATION INFORMATION

This application claims priority to Patent Cooperation Treaty Application Number PCT/EP2005/056316 filed Nov. 29, 2005, which claims priority to German Application DE 20 2004 018 469.9 filed Nov. 29, 2004, both of which contents are incorporated herein by reference.

NOTICE OF COPYRIGHTS AND TRADE DRESS

A portion of the disclosure of this patent document contains material which is subject to copyright protection. This patent document may show and/or describe matter which is or may become trade dress of the owner. The copyright and trade dress owner has no objection to the facsimile reproduction by anyone of the patent disclosure as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright and trade dress rights whatsoever.

BACKGROUND

1. Field

This disclosure relates to a low temperature cryostat.

2. Description of the Related Art

It is conventional to make use in low temperature microscopy of sample tubes in which the respective microscope is arranged. The sample tubes are inserted into 4K cryostats and cooled by means of liquid nitrogen (77K) and liquid helium (4K). A so-called dipstick with a sample to be examined and a microscope is inserted into the sample tube and cooled. The sample tube itself can in this case be evacuated or be filled with exchange gas for the purpose of better thermal coupling to the liquid nitrogen and the liquid helium.

FIG. 6 shows such a conventional arrangement having a cryostat vessel 302 that is evacuated. A cooling device 304 and a microscopy device 306 are arranged in the cryostat vessel 302. The cooling device 304 comprises a nitrogen cooler 310 with liquid nitrogen as coolant. The nitrogen cooler 310 is connected to a 70K cold shield 314 via a thermal 70K coupling 312. Arranged concentrically in the nitrogen cooler 310 with 70K cold shield 314 is a helium cooler 320 that is thermally coupled to a 4K cold shield 324 via a 4K coupling 322. A sample tube 330 is arranged concentrically relative to the helium cooler 320 with 4K cold shield 322, and relative to the nitrogen cooler 310 with 70K cold shield 314. The thermal connection between the sample tube 330 and the nitrogen cooler 310 and/or the helium cooler 320 is performed by a mechanical, and therefore thermal connection of the sample tube 330 to the 70K coupling 314 and/or the 4K coupling 324. A sample rod or dipstick 332 is inserted into the sample tube 330, and a confocal microscope 334 is arranged at its lower end.

Cooling with the aid of liquid nitrogen and liquid helium is disadvantageous in this known apparatus, since handling liquid nitrogen and liquid helium is complicated and awkward. Moreover, the use of liquid helium is expensive.

It is therefore an object of the present invention to specify a low temperature cryostat that is easier to handle and more cost-effective in operation.

This object is achieved by means of a low temperature cryostat in accordance with the features of claim 1.

Further details, features and advantages of the invention emerge from the following description of preferred embodiments of the invention with the aid of the drawings, in which:

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a first embodiment of the invention having a single-stage pulse tube cooler;

FIG. 2 shows a second embodiment of the invention having a two-stage pulse tube cooler;

FIG. 3 shows a detailed illustration of the confocal microscope of the second embodiment of the invention having a piezo positioning apparatus;

FIG. 4 shows a detailed illustration, corresponding to FIG. 3, of a third embodiment of the invention having an atomic force or scanning tunneling microscope instead of the confocal microscope;

FIG. 5 shows a fourth embodiment of the invention having a ADR cooling stage, a 100 mK cooling stage and a confocal microscope;

FIG. 6 shows a low temperature cryostat according to the prior art.

DETAILED DESCRIPTION

Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and methods disclosed or claimed.

Since it is impermissible in low temperature microscopy to transmit vibrations onto the sample, there has so far been no use of mechanical cooling devices such as compressors and pulse tube coolers. Compressor cooling devices have a broad spectrum of vibrations from the low frequency up to the high frequency range, and are therefore unsuitable as a replacement for nitrogen/helium coolers. Given appropriate design, pulse tube coolers can certainly be configured because of vibration, but their functionality dictates that they have vibrations in the low frequency 1 Hz range that cannot be eliminated. These vibrations originate from the oscillating gas column in the pulse tube cooler. These vibrations cause a deflection of the cold head of the pulse tube cooler in the □m region. The use of pulse tube coolers has so far been refrained from because of these vibrations that cannot be eliminated. However, it has been shown that when use is made of pulse tube coolers these low frequency vibrations are by far less disturbing than assumed. This is likely to be ascribed to the fact that the microscope device connected to the cold head covibrates synchronously because of the low frequencies, and this oscillation is therefore not disturbing.

In accordance with an advantageous refinement of the invention, the component of a pulse tube cooler that still most readily also generates high frequency vibrations in addition to the low frequency vibrations, specifically the turning valve, is arranged outside the cryostat vessel and is connected to the latter by means of a flexible hose line. This prevents the high frequency vibrations from impairing the mode of operation of the microscopy device, and at the same time the low frequency vibrations are reduced. Consequently, it is only the low frequency vibrations that still occur in the cryostat vessel on the basis of the oscillating gas.

In accordance with a further preferred refinement of the invention, the thermal coupling of the microscopy device to the pulse tube cooling system is designed in an elastic and vibration damping fashion. Consequently, the low frequency vibrations still occurring from the pulse tube cooling system are strongly damped and are therefore less able to have a disturbing effect on the microscopy device. Moreover, account is thereby taken of the unavoidable changes in length between ambient temperature and the temperature of the sample.

Such a low temperature cryostat can be used with a multiplicity of different microscopy devices such as confocal microscope, tunneling microscope, atomic force microscope, magnetic microscope, chemical microscope etc.

The remaining subclaims relate to further advantageous refinements of the invention.

FIG. 1 shows a schematic of the essential components of a first embodiment of the invention, in the case of which the basic concept of the invention is concerned. A cooling device 4 in the form of a single-stage pulse tube cooler 10 is arranged in a cryostat vessel 2. The pulse tube cooler 10 comprises a pulse tube 12 and a regenerator 14 that are arranged between a cold head 16 and a valve head 18. A microscopy device 6 is mechanically and thermally coupled to the cold head 16 by means of a thermal coupling 8.

FIG. 2 shows a second embodiment having a cryostat vessel 102, a cooling device 104, arranged in the cryostat vessel 102, in the form of a two-stage pulse tube cooling system 110. The pulse tube cooling system 110 has a first pulse tube cooler 111 and a second pulse tube cooler 121. The first pulse tube cooler 111 has a first pulse tube 112 and a first regenerator 113. The first pulse tube 112 and the first regenerator 113 are arranged between a valve head 114 and a 60K cold head 115. The second pulse tube cooler 121 has a second pulse tube 122 and a second regenerator 123. The second pulse tube 122 is arranged between the valve head 114 and a 4K cold head 125, and the second regenerator 123 is arranged between the 60K cold head 115 and the 4K cold head 125. A ballast volume 116 is directly connected to the valve head 114 arranged outside the cryostat vessel 102. The valve head 114 and the ballast volume 116 are connected to a turning valve 118 via a flexible hose 117.

Arranged in the cryostat vessel 102 is a sample tube 130 that is accessible from the outside and into which a sample rod 132 can be inserted. The sample rod 132 has a warm end 134, which projects from the cryostat vessel 102, and a cold end 136, which comes to lie in the interior of the cryostat vessel 102. A confocal microscope 138 is arranged in the region of the cold end 136 of the sample rod 132.

The sample tube 130, and thus the sample rod 132 with the confocal microscope 138 are connected thermally to the 60K cold head 115 via a 60K coupling 140, and to the 4K cold head 125 of the cooling device 104 via a 4K coupling 142. The 60K coupling 140 is arranged closer at the warm end 134, and the 4K coupling 142 is arranged in the region of the cold end 136. The sample rod 132 is arranged concentrically in the sample tube 130. The sample tube 130 has a hollow cladding 144 that can be evacuated or filled with exchange gas.

Owing to the spatially separated arrangement of the turning valve and its connection to the valve head via a flexible hose 117, vibrations of the turning valve 118 are strongly damped, and scarcely any vibrations are transmitted onto the cryostat vessel. Owing to the configuration of the 60K coupling 140 and of the 4K coupling 142 in the form of an elastic strip made from material that effectively conducts heat, vibrations from the pulse tube cooling system are likewise strongly damped, and so scarcely any vibrations are transmitted onto the sample tube 130, and thus onto the confocal microscope 138. A braided ground strap made from electrolytic copper is well suited therefor.

FIG. 3 shows a detail of the third embodiment of the invention, specifically the cold end 136 of the sample rod 132 with the confocal microscope 138. The confocal microscope 138 comprises a lens arrangement 146 that is thermally and mechanically connected to the 4K coupling 142 by means of a piezo positioning apparatus 148. A sample 150 to be examined is arranged below the lens arrangement 146. The light that originates from a light source (not illustrated), is reflected by the sample 150 and falls into the lens arrangement 146 is guided out of the cryostat vessel 102 via an optical fiber 152. The viewing light is preferably likewise coupled in via the optical fiber 152. The focusing of the lens arrangement 146 is performed by the piezo apparatus 148. The lens arrangement 146 can be moved and positioned on three spatial axes relative to the sample 150 with the aid of the piezo positioning apparatus 148. The entire arrangement is surrounded by a cladding 154 that is part of the sample rod 132.

FIG. 4 shows a detail of a third embodiment of the invention, in the case of which instead of a confocal microscope an atomic force or scanning tunneling microscope 160 is provided in the cryostat design according to FIG. 2. Components are correspondingly provided with the same reference numerals in FIGS. 3 and 4. The third embodiment of the invention differs from the second embodiment only in that a carrier unit 162 for a scanning tip 164 is provided instead of the lens arrangement 146, and an electric signal line 166 is provided instead of the light guide 152.

FIG. 5 shows a fourth embodiment of the invention having a cryostat vessel 202 in which a cooling device 204 is accommodated. The cooling device 204 arranged in the cryostat vessel 202 comprises a two-stage pulse tube cooling system 210 having a first pulse tube cooler 211 with a first cold head 215, and a second pulse tube cooler 221 with a second cold head 225. The interface to the outside is provided via a valve head 214. The remaining components such as turning valve and ballast volume, for example, are not illustrated. The two-stage pulse tube cooling system 210 comes close to the pulse tube cooling system from FIG. 2. The two-stage pulse tube cooling system 210 precools an adiabatic demagnetization cooling stage or an ADR cooling stage 205, having a magnet that is not, illustrated, to approximately 4K. The ADR stage 205 is thermally and mechanically coupled to the second cold head 225 of the two-stage pulse tube cooling system 210 The confocal microscope 238 with positioning apparatus (not illustrated) is arranged at the magnet (not illustrated) of the ADR cooling stage 205. The confocal microscope 238 is thereby thermally coupled to the second cold head 225 and is cooled to approximately 4K. The ADR cooling stage 205 cools to approximately 100 mK. A sample 208 is thermally coupled to the ADR cooling stage 205 via a sample holder 206, such that the sample is cooled to approximately 100 mK.

The above-described embodiments of the invention may also be combined with one another. It is likewise possible, for example, to arrange a number of different microscopes in the cryostat vessel.

LIST OF REFERENCE NUMERALS

-   2 Cryostat vessel -   4 Cooling device -   6 Microscopy device -   8 Thermal coupling -   10 Pulse tube cooler -   12 Pulse tube -   14 Regenerator -   16 Cold head -   18 Valve head -   102 Cryostat vessel -   104 Cooling device -   110 Two-stage pulse tube cooling system -   111 First pulse tube cooler -   112 First pulse tube -   113 First regenerator -   114 Valve head -   115 60K cold head -   116 Ballast volume -   117 Flexible hose -   118 Turning valve -   121 Second pulse tube cooler -   122 Second pulse tube -   123 Second regenerator -   125 4K cold head -   130 Sample tube -   132 Sample rod -   134 Warm end of 132 -   136 Cold end of 132 -   138 Confocal microscope -   140 60K coupling -   142 4K coupling -   144 Cladding of 130 -   146 Lens arrangement -   148 Piezo apparatus -   150 Sample -   152 Optical fiber -   160 AFM or scanning tunneling microscope -   162 Carrier unit for 164 -   164 Scanning tip -   166 Electric signal line -   202 Cryostat vessel -   204 Cooling device -   205 ADR cooling stage -   206 Sample holder -   208 Sample -   210 Two-stage pulse tube cooling system -   211 First pulse tube cooler -   214 Valve head -   215 First cold head -   221 Second pulse tube cooler -   225 Second cold head -   238 Confocal microscope -   302 Cryostat vessel -   304 Cooling device -   306 Microscopy device -   310 Nitrogen cooler -   312 70K coupling -   314 70K cold shield -   320 Helium cooler -   322 4K coupling -   324 4K cold shield -   330 Sample tube -   332 Sample rod (dipstick) -   Closing Comments

The foregoing is merely illustrative and not limiting, having been presented by way of example only. Although examples have been shown and described, it will be apparent to those having ordinary skill in the art that changes, modifications, and/or alterations may be made. 

1. A low temperature cryostat having a cryostat vessel, a cooling device, arranged in the cryostat vessel, for producing a cooling temperature level TK, a microscopy device for examining a sample, and at least one thermal coupling for thermally and mechanically connecting the microscopy device to the cooling device, wherein the cooling device comprises a pulse tube cooling system.
 2. The low temperature cryostat as claimed in claim 1, wherein the pulse tube cooling system comprises a turning valve that is arranged outside the cryostat vessel and is connected to the cryostat vessel via a vibration damping line.
 3. The low temperature cryostat as claimed in claim 2, wherein the vibration damping line is a flexible connecting hose.
 4. The low temperature cryostat as claimed in one of the preceding claims, wherein the pulse tube cooling system is a single-stage pulse tube cooler.
 5. The low temperature cryostat as claimed in one of the preceding claims 1, wherein the pulse tube cooling system comprises a multistage, in particular two-stage pulse tube cooler.
 6. The low temperature cryostat as claimed in claim 1, wherein the thermal coupling of the microscopy device to the pulse tube cooling system is designed in an elastic and vibration damping fashion.
 7. The low temperature cryostat as claimed in claim 1, wherein the microscopy device is arranged in a sample tube.
 8. The low temperature cryostat as claimed in claim 7, wherein the sample tube can be inserted into the cryostat vessel and can be thermally coupled to the cooling device via the thermal coupling.
 9. The low temperature cryostat as claimed in claim 1, wherein the cooling device comprises a first cooling stage in the form of said pulse tube cooling system, and a second cooling stage for a cooling temperature level in the range <4K, and wherein the second cooling stage is precooled by the first cooling stage.
 10. The low temperature cryostat as claimed in claim 9, wherein the second cooling stage has an adiabatic demagnetization device or a 3 He/4 He dilution cooler or a 3 He cooler or a mechanical cooling device such as a helium compressor cooler, or an electric cooling device such as a Peltier element or a superconducting tunnel diode such as an NIS diode.
 11. The low temperature cryostat as claimed in claim 1, wherein the microscopy device comprises a confocal microscope.
 12. The low temperature cryostat as claimed in claim 1, wherein the microscopy device comprises a scanning tunneling microscope.
 13. The low temperature cryostat as claimed in claim 1, wherein the microscopy device comprises an atomic force microscope. 